Index-guided semiconductor lasers have proven to be useful devices. Index guiding refers to the use of variations in the optical index of refraction between material layers to provide for optical confinement. To fabricate an index-guided semiconductor laser one must use a suitable material system, create an active region, and provide for carrier confinement, radiation confinement, and optical feedback. Modern semiconductor lasers may fulfill these requirements using a heterostructure formed in a suitable material system (such as AlGaInP, AlGaAs, or InGaAsP), a lateral waveguide which provides for optical confinement, and an optical Fabry-Perot cavity formed from cleaved facets.
The following uses the subscripted notation, A.sub.M L.sub.N, where the nonsubscript terms (A and L) designate a material (be it an element or a compound) and the subscripted terms (M and N) designate the atomic concentration of their associated material. Additionally, parenthesis are used to identify compounds which act together. For example, the notation (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P implies that half of the material is phosphorous, one quarter is comprised of indium, and the remaining quarter is a compound of aluminum and gallium in which the composition takes a range (0.ltoreq.X.ltoreq.1) from all aluminum (the subscripted X is equal to 1) to all gallium (the subscripted X is equal to 0). It is to be understood that the subscripted terms are, in practical materials, only approximations. For example, in a material designated as (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P, the subscripted percentages X and 0.5 may vary slightly (such as by .+-.0.05). The general alloy (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P) will be denoted AlGaInP for convenience.
An important semiconductor laser material system, and one which is particularly useful for fabricating visible light emitting semiconductor lasers, is (Al.sub.x Ga.sub.1-x).sub.0.5 In.sub.0.5 P. That material system lattice matches with GaAs substrates and can be grown using organometallic vapor phase epitaxy (OMVPE). Interestingly, OMVPE-grown AlGaInP exhibits two distinct phases: an ordered phase, consisting of a monolayer InP/Al.sub.x Ga.sub.1-x P superlattice formed by spontaneous atomic organization during growth and characterized by a lower bandgap; and a random-alloy phase with no ordering on the group III sublattice but with a higher bandgap energy. Importantly, the lower bandgap phase occurs when AlGaInP is OMVPE grown on substantially (001) orientated substrates, while the higher bandgap phase occurs when AlGaInP is OMVPE grown on substrates whose surfaces are misorientated from (100) toward (111)A, such as at angles of between 5 degrees relative to the substrate's surface and the (111)A plane.
It would be useful to have index-guided semiconductor lasers which achieve index-guiding using phase differences which result from the growth of material on different crystalline planes. It would be particularly useful to have such index-guided semiconductor lasers which emit light in the visible spectrum.